Elapsed time indicator



Jan- 28, 1964 M. A. BLUMENFELD ETAL 3,119,754

ELAPSED TIME INDICATOR Filed Feb. 10, 1961 D sa RF MN NE EM VU mm. A. L my. T

N ME M l A rOR/VEY United States Patent O 3,119,754 ELAPED Thrill ENDCATR Martin A. Blumenfeld, Somerville, NJ., and Lien Yen lLi, Glen Cove, NX., assignors to Sperry lian-d Corporation, Great Neelix, Nfl-.7., a corporation of lllelaware Filed Feb. il), Qui, Lier. No.. 88,4% 5 Claims. (Cl. 294-52) The present invention generally relates to elapsed time indicators of the electrolytic cell type and, more particularly, to such an indicator suitable for use over relatively wide temperature ranges.

Elapsed time indicators of the electrolytic cell type are well known in the art as comprising an anode element, a cathode element and an electrolytic solution housed in a sealed container. The cell is energized by causing a constant direct current to ilow between the anode and cathode elements during the time interval to be measured. While the current is llowing, metal is transferred at a predetermined rate from the anode to the cathode of the electrolytic cell. The total elapsed time is directly related to the erosion of the anode and can be easily measured by Calibrating the length of the anode element.

One of the primary uses of the electrolytic cell is to measure the length of time that electrical equipment has been in operation so that preventative maintenance procedures can be undertaken at proper intervals. For this purpose, the cell is energized concurrently with said equipment. A problem arises, however, when the electrolytic cell is subjected to extreme temperature variations such as are encountered during the flight of present day high altitude aircraft. Temperature changes of such magnitude adversely affect the accuracy of the elapsed time indication and can actually destroy the cell.

lt is oi course desirable that the plating action on which the elapsed time indication is based be substantially independent of temperature. More particularly, it is necessary that an electrolytic solution be provided which satisfies the following requirements over the entire temperature range ot operation such as, tor example, from 55 C. to 110 C. The solution must facilitate the sound deposition of metal on the cathode element of the electrolytic cell. Both anode and cathode eiiiciency should approach 100 percent. Gassing of thc solution and anode sludging should be kept to a minimum. Anode erosion must be relatively uniform and in accordance with Faradayls laws. The solution must remain liquid throughout the temperature range.

A cursory consideration of the problem might suggest merely adding conventional antifreeze agents such as alcohol or ethylene glycol to prior art electrolytic solutions to achieve the required low temperature operation. lt has been found, however, that when such agents are added to a copper iluoborate electrolytic solution, considerable salting out occurs at the low temperatures. Moreover, the addition of organic agents such as methyl ethyl alcohol seriously impede plating at high temperatures because of the low boiling points oi the addi- `ives.

In accordance with the present invention, the aforementioned requirements are met directly by a unique proportioning of the prior art copper iluoborate electrolytic solution constituents. No additives foreign to the original solution are required.

lt is the principal object of the present invention to provide an improved electrolyte for an elapsed time indicator of the electrolytic cell tyle suitable for use over wide variations in temperature.

Another object of the present invention is to provide an improved elapsed time indicator of the electrolytic cell type for use over relatively wide temperature ranges.

ice

A further object is to provide an electrolytic solution for electro-depositing copper at a rate which is substantially independent or temperature over a wide range.

These and other objects of the present invention, as will appear from a reading of the following specification, are achieved in a preferred embodiment by the provision of an electrolytic cell comprising a copper anode, a copper cathode and an electrolytic solution housed in a sealed glass envelope. Means are provided for passing a constant current through the anode and cathode elements whereupon metallic copper is eroded from the anode and deposited upon the cathode. The rate of metallic copper transference from the anode to the cathode is maintained substantially independent of temperature over a range from about 55 C. to about 110 C. through the use of an appropriately proportioned copper luorborate solution.

The copper uoborate solution consists of copper iluoborate Cu(BF4)2, boric acid (lelgBOg), 'luoboric acid (HBFi), and distilled water. ln accordance with the present invention, the ratio in weight of copper iuoborate to boric acid is substantially 15:1. The relationship between the copper tluoborate, iluoboric acid and water is determined substantially in accordance with the linear expression:

Where y represents CMBFQZ as measured in grams per liter ot elcctrolytic solution and x represents the ratio in weight of H1354 to H2O.

For a more complete understanding of the present invention, reference should be had to the following specilication and to the ligures of which:

FIG. 1 is a simplified schematic diagram of an elapsed time indicator of the electrolytic cell type; and

FlG. 2 is a plot of the relationship between the copper fluoborate, uob-oric acid and water constituents of the electrolytic solution as determined in accordance with the present invention.

Referring to FlG. 1, the elapsed time indicator comprises a high silicon glass envelope l which is adapted at opposite ends 2 and 3 for the insertion of conductors 4 and 5. Conductors i and 5 are sealed to glass envelope ll by means of a suitable glass-to-metal seal 9 such as Kovar. Conductor l supports tubular glass guide o which encases high-purity (Qiagen-free) copper anode 7. A direct electrical connection is made between conductor l and anode '7. Cathode 8 comprises essentially the same high-purity copper as used for anode i and is supported adiacent end 3 of tube l by conductor 5. A direct electrical connection is made between cathode S and conductor 5.

Substantially all ot the remaining volume contained within envelope l is filled with a copper iluoborate electrolytic solution 1l. It is preferred to prevent exposure of conductors d and 5 to solution lll. by covering the conductors with glass itl along those portions which are interior to envelope l. An expansion chamber or protrusion l2 is provided to allow for the expansion of solution il at elevated temperatures. Solution ll only partially fills chamber l2 leaving an entrapped volume of air i3 which is compressed upon the expansion of solution l1.

rEhe basic operation oi the electrolytic cell is well known in the art. Briefly, it involves the passing oi an essentially constant DC. current between conductors 4 and 5. The resulting transference of the metallic copper from anode to cathode proceeds at a uniform rate. A series of tiducial marks lli which may, for example, be inscribed on the wall ot glass envelope i, marks oil the length oi anode 7. The marks lli may be used to measure the remaining length of anode 7 at any time during the operation of the electrolytic cell. The remaining length of anode 7 is a measure of the amount of anode erosion which, in turn', is proportional to the length o time that the DC. current has been applied between conductors i and 5. Thus, where the application of the D.C. current is commensurate with the time that specied electrical apparatus is energized, the total operational time of said apparatus may be determined by reading the remaining length of anode 7.

In accordance with the present invention, the electrolytic cell of FIG. 1 is adapted for operation over a temperature range from about 55 C. to about 110 C. This is accomplished by proportioning the constituents of copper iluoborate solution 11i in the following manner. The copper fluoborate solution consists of copper uoborate [Cu(Bi-`4)2], iluoboric acid (HBH), distilled water, and boric acid (H3BO3). The ratio in weight of Cu(BF4)2 to H3303 is about 15:1. The relationship between Cu(BF4)2, HBH and H2O is determined substantially in accordance with the expression y= 940x{640 where y represents Cu(BF4)2 as measured in grams per liter of electrolytic solution, and x represents the ratio in weight of HEP., to H2O. This relationship is represented in graphical form in the plot of FIG. 2.

Referring to FG. 2 which is a plot of the expression y= 940x+640, it has been found that the relationship between the copper luoborate, iiuoboric acid and water must be such as to define points along the straight line. Solutions which may be represented by points lying above the line exhibit too high a specific resistance especially at low temperatures. Solutions represented by points lying below the line tend to salt out or freeze or both at the low temperatures. Additionally, the concentration of copper liuoborate in grams per liter of electrolytic solution should be no greater than approximately 430 and no less than approximately 40. A concentration or greater than 430 grams per liter produces a tendency of the solution to salt out at low temperatures whereas a concentration less than 40 grams per liter seriously weakens the eiciency of the transference of copper between the anode and cathode elements at all temperatures. However, when the relationship between copper fluoborate, iiuoboric acid and water is such as to dene points substantially along the straight line of FTG. 2 between the ordinates of 430 and 40 grams per liter, and the ratio of copper fluoborate to boric acid is maintained at about 15:1, a solution is produced which facilitates the eiiicient operation of the elapsed time indicator of FIG. 1 substantially independent oi temperature over the range between 55 C. and 110 C.

A typical iiuoborate electrolytic solution, prepared in accordance with the present invention, consists oi the following proportions ot the constituents,

Constituent: Gm./liter Cu(BF4)2 166 HB 4 392 Distilled H2O 775 H3BO3 11.1

In the above example, the ratio of Cu(BF4)2/H2O is substantially 0.506. These proportions define point P in the plot of FIG. 2.

While the invention has been described in its preferred embodiments, it is understood that the words which have been used are words of description rather than of limita tion and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An electrolytic solution for use in an elapsed time indicator of the electrolytic cell type havingcopper anode and cathode elements, said solution comprising copper 4 fluoborate of a concentration in the range from about 40 to about 430 grams per liter, boric acid, liuoboric acid and water, the ratio in weight of copper iluoborate to boric acid being about 15 :1 and the relationship between the copper fiuoborate, luoboric acid and water being determined substantially in accordance with the expression:

wherein y represents the weight in grams of said copper iluoborate per liter of electrolytic solution and x represents the ratio in weight of luoboric acid to water.

2. An electrolytic cell comprising an anode element, a cathode element, an electroiytic solution, and a sealed container for housing said elements and said solution, said electrolytic solution comprising copper i'luoborate of a concentration in the range from about 40 to about 430 grams per liter, boric acid, iiuoboric acid and water, the ratio in weight of copper iiuoborate to boric acid being about 15:1 and the relationship between the copper iiuoborate, iiuoboric acid and water being determined substantially in accordance with the expression:

wherein y represents the weight in grams of said copper fiuoborate per liter of electrolytic solution and x represents the ratio in weight of iluoboric acid to water.

3. An electrolytic cell comprising a copper anode, a copper cathode, an electrolytic solution, and a sealed glass envelope for containing said anode, said cathode and said solution, said solution comprising copper fluoborate of a concentration in the range from about 40 to about 43() grams per liter, boric acid, iiuoboric acid and water, the ratio in weight of copper iiuoborate to boric acid being about 15:1 and the relationship between the copper iluoborate, iluoboric acid and water being determined substantially in accordance with the expression:

wherein y represents the weight in grams of said copper iluoborate per liter of electrolytic solution and x represents the ratio in weight of fluoboric acid to water.

4. An electrolytic solution for electrodepositing copper at a rate which is substantially independent of temperature over a range from about 55 C. to about 110 C., said electrolytic solution comprising copper luoborate of a concentration in the range from about 4() to about 430 grams per liter, boric acid, fluoboric acid and water, the ratio in weight of copper iiuoborate to boric acid being about 15:1 and the relationship between the copper iluoborate, iiuoboric acid and water being determined substantially in accordance with the expression:

wherein y represents the weight in grams of said copper fluoborate per liter or electrolytic solution and x repre-` References Cited in the le of this patent UNITED STATES PATENTS Re. 24,190 Kroko July 31, 1956 2,791,473 Mattox May 7, 1957 3,029,384 Hart Apr. 10, 1962 OTHER REFERENCES Handbook of Practical Elcctroplating, page 154, Macmillan Co., New York, 1959. 

4. AN ELECTROLYTIC SOLUTION FOR ELECTRODEPOSITING COPPER AT A RATE WHICH IS SUBSTANTIALLY INDEPENDENT OF TEMPERATURE OVER A RANGE FROM ABOUT -55*C. TO ABOUT 110*C., SAID ELECTROLYTIC SOLUTION COMPRISING COPPER FLOBORATE OF A CONCENTRATION IN THE RANGE FROM ABOUT 40 TO ABOUT 430 GRAMS PER LITER, BORIC ACID, FLUOBORIC ACID AND WATER, THE RATIO IN WEIGHT OF COPPER FLUOBROD TO BORIC ACID BEING ABOUT 15:1 AND THE RELAATIONSHIP BETWEEN THE COPPER FLUOBRORATE, FLUOBORIC ACID AND WATER BEING DEFINED SUBSTANTICALLY IN ACCORDANCE WITH THE EXPRESSION: 